A new feature related to some spreadsheet applications is the ability for multiple users to collaborate on a single spreadsheet file simultaneously in real time. This is a mode of editing where each user can instantaneously (or almost instantaneously) see changes made by other users who are editing the file. For example, when a first user makes a change to a spreadsheet cell, all other users may have their view of the spreadsheet updated milliseconds later so that all changes seem to appear as they happen. There are often other features that go along with this type of collaboration such as real time chat and user presence information. If implemented well, this feature truly creates the appearance that users are working together on the same spreadsheet, sharing and editing data at the same time.
One problem associated with real time collaboration is that, in most scenarios, each collaborating user wants to see the same data in the spreadsheet file. This is a clear user expectation, and, if users don't see the same data after they make changes, they will feel like the data is incorrect, or that their changes weren't received properly. The users may also become uncertain as to who has the ‘right’ data. Since this user expectation is core to the user experience, calculations in conventional real time collaboration environments are performed at a central location such as a server and then broadcast to each client separately. This is because different calculations made at different times can cause the data to be different in many cases. Thus, every time a user makes a change, the change is broadcast, and the spreadsheet file is recalculated and rebroadcast so that every client version of the spreadsheet file can be updated. Doing this takes time, and is particularly slow for spreadsheets that have more complex calculations.
Another problem associated with real time collaboration is that collaborating users will often want to see their own unique view of the data. For example, when users are entering data into a single large table, each user may have entries that only the individual user cares about seeing. Each individual user may want to filter the table in a unique way so that only the entries that the individual user is responsible for are shown. The problem is that each user typically has a different filter to be applied to the same table, but, since each user is editing the same table at the same time, they all see each other's changes. This traditionally has made manipulating or analyzing data in a real time collaborative environment very difficult if not impossible.